The present invention is generally directed to electrostatographic carrier compositions and processes for stabilizing the triboelectric charge properties and the conductivity properties of the carrier compositions over extended periods of time and under highly variable humidity conditions. More specifically, the present invention is directed to carrier compositions comprising a core with a coating thereover comprised of at least one polymer, a conductive component such as a colorant or conductive pigment; and a stabilizer compound, wherein the triboelectric charge properties and the conductivity properties of the coated carrier particles remain constant over time and under variable humidity conditions, whether the carrier composition is in use as a developer or is in storage or transport.
The composition and processes of the present invention enable, for example, carrier and developer compositions exhibiting high resistance to environmental degradation and variation, for example, oxidation or humidity, and high stability of the carrier or developer compositions when eventually used after extended periods in storage or in transport.
The prior art discloses methods of preparing coated carriers and processes for controlling the tribocharging and conductivity properties of the partially coated conductive carrier cores with electropositive or electronegative polymers, for example, as disclosed in U.S. Pat. No. 5,015,550 to Creatura et al. U.S. Pat. No. 5,236,629, to Mahabadi et al., discloses submicron polymer/carbon black composites particles prepared by suspension polymerization techniques and their use in preparing conductive magnetic brush carriers by powder coating processes. Also of interest are U.S. Pat. Nos. 5,385,796, and 5,120,628, which disclose admixtures of a conductive component, such as copper iodide, and polymers for use in electrophotoreceptor devices.
Dry polymer coating processes for carrier particles are known in the art, such as U.S. Pat. Nos. 3,590,000 (Mammino, et al.), U.S. Pat. No. 4,233,387 (Mammino, et al.), U.S. Pat. No. 4,935,326 (Creatura, et al.), U.S. Pat. No. 4,937,166 (Creatura, et al.), and U.S. Pat. No. 5,002,846 (Creatura, et al.).